The conventional image-forming process of silver halide photography includes imagewise exposure of a photographic silver halide recording material to actinic radiation (such as visible light), and the eventual manifestation of a useable image by wet photochemical processing of that exposed material. A fundamental step of photochemical processing is the treatment of the material with one or more developing agents to reduce silver halide to silver metal. With black-and-white photographic materials, the metallic silver usually comprises the image. With color photographic materials, the useful image consists of one or more organic dye images produced from an oxidized color developing agent formed wherever silver halide is reduced to metallic silver.
To obtain useful color images, it is usually necessary to remove all of the silver from the photographic element after color development. This is sometimes known as "desilvering". Removal of silver is generally accomplished by oxidizing the metallic silver, and then dissolving it and undeveloped silver halide with a "solvent" or fixing agent in what is known as a fixing step. Oxidation is achieved using an oxidizing agent, commonly known as a bleaching agent. For some processing methods, these two steps can be performed in the same processing step in what is known as bleach-fixing.
Common bleaching agents include ferric salts and ferric complexes of various polycarboxylic or polyaminopolycarboxylic chelating ligands. Common fixing agents include thiosulfate salts (both ammonium and sodium thiosulfate salts) and thiocyanates.
Color photographic silver halide materials often contain various spectral sensitizing dyes that extend the inherent photosensitivity of the photosensitive silver halide emulsions to electromagnetic radiation. One important class of such spectral sensitizing dyes includes carbocyanine sensitizing dyes that are commonly included in silver halide emulsion layers in photographic silver halide films. For example they are often present in color reversal photographic silver halide films (films normally used to provide color positive images).
Many photographic silver halide elements contain residual spectral sensitizing dyes after photoprocessing. In some cases, the level of retained spectral sensitizing dyes is inconsequential and thus, unobservable. In other instances, however, the high level of retained spectral sensitizing dye results in undesirably high dye stain (or unwanted color) in the elements. This dye stain problem is aggravated when the silver halide elements are designed for shorter wet processing times, or when certain silver halide emulsions are used that require higher concentrations of spectral sensitizing dyes.
A number of solutions have been proposed for this problem, including the inclusion of common water-soluble stilbene optical brighteners, such as diaminostilbene compounds, in various photographic processing compositions. For example, such compounds are known to be used in color developer compositions [as described for example, in Research Disclosure, 20733, page 268, July, 1981 and U.S. Pat. No. 4,587,195 (Ishikawa et al) and as commonly used in the commercial Process RA-4 color developing compositions available from a number of manufacturers], bleach-fixing compositions [as described for example, in JP 1-062642 (published Mar. 9, 1989), JP 1-158443 (published Jun. 21, 1989), and U.S. Pat. No. 5,043,253 (Ishikawa)], or dye stabilizing compositions used at the end of the color photographic photoprocessing [as described for example in U.S. Pat. No. 4,895,786 (Kurematsu et al)].
In addition, it has been proposed to include stilbene optical brighteners in sodium ion containing fixing solutions to solve the problem with retained spectral sensitizing dye, as described in Research Disclosure 37336, page 340, May 1995. Such fixing solutions have sodium ions as the predominant cation because of the environmental concerns presented by ammonium ions. However, the presence of sodium ions slows down the fixing process, and this reduction in photoprocessing speed may be unacceptable in some instances. A reduction or elimination of the sodium ions for that reason may be required when certain films (such as color reversal films) are being processed.
It has also been observed that when the noted stilbene compounds were added to conventional ammonium ion containing fixing solutions at appropriate concentrations needed to reduce dye stain, the stilbene compounds were not stable over a desired shelf life. The stilbene compounds stayed in solution for a brief time after mixing, but upon storage for only a few hours, the solutions exhibited considerable precipitation. In fact, the Research Disclosure publication 37336 (noted above) also suggests that stilbene compounds are incompatible in fixing solutions containing high ammonium ion concentration. Thus, it would appear that there is no incentive for a skilled worker in the photographic industry to use common triazinylstilbene optical brighteners in fixing solutions containing high ammonium ion content. One such triazinylstilbene compound is known commercially as PHORWITE REU (also sometimes known as BLANKOPHOR REU, available from Bayer), and another commercially known stilbene is TINOPAL (available from Ciba).
In addition, many optical brighteners known in the art have limited solubility in aqueous processing compositions, especially concentrated compositions. Thus, their usefulness is limited. In addition, the inherent strong fluorescence of these compounds becomes a liability and limits their usefulness in instances where they cannot be completely removed from the system.
There remains a need in the photographic industry for a way to decrease the stains resulting from spectral sensitizing dyes retained during photoprocessing without the problems noted above. In particular, there is a need for sensitizing dye stain reducing compounds that are more stable in various processing compositions.